Gels for protecting metal structures

ABSTRACT

-(2,4,6-TRI(O=),5-(-)-HEXAHYDRO-1,3,5-TRIAZIN-1,3-YLENE)M-   -(2,4,6-TRI(O=),5-X-HEXAHYDRO-1,3,5-TRIAZIN-1,3-YLENE)N-   -(R)(2M+N+1)- -(A)(M+2)   1. A PROESSS FOR PROTECTING METALLIC OBJECTS FROM CORROSION COMPRISING INTRODUCING BETWEEN THE SURFACE OF SAID METALLIC OBJECTS AND THE SOURCE OF SAID CORROSION, A GEL COMPOSITION SUBSTANTIALLY INSOLUBLE IN WATER PREPARED BY CONTACTING, AT A PH 7, A GEL FORMED BY REACTING ABOUT 1.0 TO ABTO ABOUT 10% BY WEIGHT OF POLYVINYL ALCOHOL OR A PRECURSOR THEREOF AT A PH ABOVE 7 WITH FORM ABOUT 0.5 TO ABOUT 50% BY WEIGHT OF A SALT OF A POLYMERIC ISOCYANURIC ACID,WHEREIN SAID SALT OF A POLYMERIC ISOCYANURIC ACID HAS THE CHEMICAL STRUCTURE:   -(2,4,6-TRI(O=),5-(-)-HEXAHYDRO-1,3,5-TRIAZIN-1,3-YLENE)M-   -(2,4,6-TRI(O=),5-X-HEXAHYDRO-1,3,5-TRIAZIN-1,3-YLENE)N-   -(R)(2M+N+1)- -(A)(M+2)   WHEREIN: R=DIVALENT HYDROCARBON OR SUBSTITUTED HYDROCARBON RADICAL, CONTAINING 2 TO ABOUT 40 CARBON ATOMS, X IS SELECTED FROM THE GROUP CONSISTING OS GROUP I METALS, GROUP II METALS, HYDROGEN, AND QUATERNARY AMMONIUM RADICALS, A IS A MONOVALENT ORGANIC RADICAL ELECTED FROM THE GROUP CONSISTING OF -NCO, -NHCO2 R&#39;&#39;, -NHCO NHR&#39;&#39; -NH2-NHR&#39;&#39;, NR&#39;&#39;2, AND R&#39;&#39;, WHEREIN R&#39;&#39; IS A MONOVALENT HYDROCARBON RADICAL OR SUBSTITUTED HYDROCARBON RADICAL CONTAINING FROM 1 TO ABOUT 40 CARBON ATOMS, WHEREIN M IS THE AVERAGE NUMBER OF TRISUBSTITUTED ISOCYANURATE RINGS PER MOLECULE AND IS A POSITIVE NUMBER FROM ZERO HYDROCARBON RADICAL CONTAINING FROM 1 TO ABOUT 40 N IS THE AVERAGE NUMBER OF ISOCYANURATE ACID AND/OR IS ISOCYANURATE SALT GROUPS AND IS A POSITIVE NUMBER FROM ABOVE 1 TO ABOUT 10,000, WHEREIN 2M+N+1=THE AVERAGE NUMBER OF DIVALENT R GROUPS AND IS A POSITIVE INTEGER FROM 2 TO ABOUT 11,0000, AND WHEREIN M+2 IS THE AVERAGE NUMBER OF A GROUPS AND IS A POSITIVE INTEGER FROM 2 TO ABOUT 2,000, AND WHEREIN THERE ARE NO N-TO-N BONDS AND N A-TO-N BONDS, AND NO A-TO-A BONDS AND NO R-TO-R BONDS.

Oct-22 1974 s. KuRTls Erm. W1

l GELS FOR PROTECTING METAL STRUCTURES Filed June 8, 1972 2 Sheets-Sheet 1 v l TNW WTO l i 0 o 2M+N+| M+2 own4| H cozcHs s-czHs ocH3 I (WHERE Hl F, Cl, Br or I) i l 9 l 1 1@ @n @H @H ?'Unitecl States Patent 3,843,374 GELS FOR PROTECTING METAL STRUCTURES Soma Kurtis, Denver, Perry A. Argabright, Larkspur, and

C. Travis Presley, Littleton, Colo., assignors to Marathon Oil Company, Findlay, Ohio Filed June 8, 1972, Ser. No. 260,843 Int. Cl. C09d 5/08 U.S. Cl. 106-14 8 Claims ABSTRACT F THE DISCLOSURE Metal structures, e.g., oil storage tanks, are protected from corrosion, e.g., by salt water or acidic ground uids, by application of a coating of a gel containing a polyvinyl alcohol (PVA) and a polyisocyanurate salt of specified structure at a pH in excess of 7. Gel can be applied to either the structure or the soil which it contacts.

CROSS REFERENCES TO RELATED APPLICATIONS The following U.S. Patent applications relate to compounds and uses which are generally related to the present invention:

Ser. Nos. 317,884 and 317,883 both filed 26 December 1972, and Ser. No. 173,892 filed 23 August 1971.

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to coatings for the prevention of corrosion of metallic objects.

Description of the Prior Art Past techniques for the protection of metal elements from corrosion have consisted mainly of removal of existing top soil and replacement with selected clean or washed sands, and low concentration oil treatments ranging from asphaltic hydrocarbons to No. 2 and similar types of oils. Complete concrete covering of the surface below the metal object, e.g., a storage tank, is used on occasion. Electrical corrosion protection has generally been provided by the application of anodes, rectiers, or periodic chemical neutralization of the corrosive liquids accumulating under or rising to the tank bottom.

The general types of gels and the prior art relating thereto are discussed in the aforementioned related applications.

The present invention combines the ease of application of the gels with the permanance of more diicult to apply conventional coatings.

SUMMARY GF THE INVENTION General Statement of the Invention According to the present invention, specific gels formed by the reaction at a pH above 7 of polyvinyl alcohol or a precursor thereof, e.g., polyvinyl acetate, with salts of polymerized isocyanuric acids, is applied in such a position as to prevent contact between a source of corrosion, e.g., soil, liquids, or corrosive gases, and the metal element to be protected. The gel may be readily coated onto the metal structure at the point where it will contact the lCe corrosive fluids or may be applied to the corrosive source itself, e.g., as in coating the surface of the soil before building a metal structure on it. Alternatively, the gels may be mixed with sand or other solid material to form a load-bearing platform which can readily be levelled t0 provide a foundation for the metal structure.

The present invention relates to a new class of compositions which are useful as gels, e.g., in forming plugs such as for pipe line separation pigs etc. These compositions are produced by contacting polyvinyl alcohol with a compound characterized by containing in a single molecule the following groups:

if 0=/N\=0 metal isocyanurate, i I

-NVN- ll O s 0:/ M wih or Without isocyanurate, l`II I Il O The gelling agents of the present invention have the `advantage of giving a controllable time to onset of gelation. That is, by merely adjusting the pH of the initial solution, the gelation time may be controlled, a feature not available with conventional systems.

The isocyanurate compounds of the present invention have the general structure shown in Fig. 1; where:

R divalent hydrocarbon or substituted hydrocarbon radical, as described below and exemplified in FIG. 2.

X a metal, or hydrogen or quaternary ammonium (which, for the purposes of this invention, acts like a metal) or a combination thereof. Particularly preferred are hydrogen, quaternary ammonium and metals selected from the following groups of the Periodic Table; Ia, Ib, IIa, IIb, Illa, IIIb, IVa, IVb, Va, Vb, Vla; including such metals as Li, Na, K, Rb, Cs, Ag, Au, Be, Mg, Ca, Sr, Ba, Ra, Zn Cd, Hg, B, Al, Sc, Y, La, and the other rare earths, Ac, Ga, In, Tl, Ti, Zr, Hf, Ge, Sn, Pb, V, Nb, Ta, Sb, Bi, Cr, Mo, W, Mn, Fe, Ru, Co, Ni, Rh, Pd, Os, and Ir.

A a monovalent orbanic radical selected from the following: isocyanate (NCO) urethane (-NHCOgR), urea (--NHCONHR), amino (-NH2, -NHR, -NR2), or R', for example.

R monovalent hydrocarbon or substituted hydrocarbon radical, as discussed below;

M average number of trisubstituted isocyanurate rings and is a positive number from 0 to about 400, and most preferably from 0 to about 200.

N average number of isocyanuric acid and/or isocyanurate salt groups and is a positive number from above 1 to about 10,000, more preferably from 2 to about 1000, and most preferably from 3 to about 100.

2M -l-N +1 I= average number of divalent R groups and is a positive integer from 2 to about 11,000, more pref- 3 erably from 3 to about 1,100 and most preferably from 4 to about 140.

M 2 average number of A groups and is a positive integer from 2 to about 2,000, more preferably from 2 to about 400, and most preferably from 2 to about 200;

| -cHlcHgom curo-CHP, oHFoH-CHP.

@-CHi-, ete.

R and/or R' can be substituted with groups that do not interfere in the products subsequent utility or in its preparation. Examples of such non-interfering groups are: -NO2, Cl, F, Br, I, CN, -CO2R, CO-R, -O-R", -SR, NR"2, -CONR2, -SO3R, -SO2R, -SOR, phenyl, naphthyl, alkyl (1 40 carbon atoms), -PO3R", cyclohexyl, cyclopropyl,

etc. Where R may be hydrogen, lower alkyl (e.g., ethyl, hexyl) or aryl (e.g., monovalent radicals corresponding to the aryl radicals described in FIG. 2. T he examples of R (shown in FIG. 2) are set forth for purposes of elucidation, not restriction.

It will be recognized that the values of M and N described above are on the basis of the integers which will be used to describe a single molecule. In actual practice, the invention will involve mixtures of molecules of the general form described above. Thus, the average value of M for the mixture may be from about 1 to about 2000, more preferably from about 1 to 400, and most preferably from about 1 to 200; the average value of N may be from about 0.5 to 10,000, more preferably from about 0.5 to 1000, and most preferably from about 0.5 to 100.

Utility of the Invention As stated above, the present invention may be utilized for the prevention of corrosion of a wide variety of metal objects subjected to a wide variety of corrosive influences. For example, in the commonly encountered instance of a metal surface, e.g., a tank bottom, being located in contact with soil which can contain corrosive liquids or solids or both, the bottob of the tank can be smeared with the gels of the present invention prior to placement on the soil. The soil itself may be coated with the present invention and the metal then placed on top of the coating. Alternatively, the soil may be mixed into the coating to provide a load-bearing platform for the solid object. Objects which may be so protected can obviously include buried pipelines, buried steel structural members, signposts, and light posts of metal, electrical conduits which are subjected to corrosive environments, aboveground metal structures which are in contact with fumes, e.g., from heating or other industrial operations, underground storage tanks, or storage tanks resting on the ground, metals exposed to marine environments (in such instances the gel must be allowed to dry so as to form a continuous or nearly continuous ring around the structure) and literally thousands of other applications.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the general formula of the polyisocyanurate starting materials of the present invention.

FIGS. 2 and 3 exemplify some of the structures of R groups of the polyisocyanurate starting materials and products of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Starting Materials: The gels of the present invention can be formulated according to the aforementioned Ser. No. 173,892 led Aug. 23, 1971. The techniques of this and the other rated applications, all of which are to be considered as incorporated herein, can be utilized with the present invention.

The starting materials for the present invention are- Salts of polyisocyanuric acids: These are produced according to the techniques taught in U.S. Pat. 3,573,259, by reacting a metal cyanate and an organic diisocyanate in the presence of an aprotic solvent to form isocyanuralte-containing polyisocyanate metal salts. Preferably 0.5 to about 50% by weight, more preferably 1.0 to about 25% by weight, and most preferably 2.0 to about 10% by weight of such salts are employed in formulating the gels.

Polyvinyl alcohol: The polyvinyl alcohol used in the present invention can be of commercial quality such as that marketed by Monsanto Company of St. Louis, Mo., under the trade-name Gelvatol. It should have a molecular weight within the range of from about 2,000 to about 250,000, more preferably from 3,000 to about 200,000, and most preferably from 10,000 to about 126,000. In general, about 1.0 to about 10.0, more preferably 2.0 to about 6.0, and most preferably 3.0 to about 5.0% by wt. of polyvinyl alcohol will be contacted with the aforementioned isocyanurate salt starting materials.

Bases: While not narrowly critical, the bases employed with the present invention will preferably be alkali metals, metal hydroxides, e.g., NaOH, KOH, LiOH, and alkaline earth metal hydroxides, e.g., Ca(OH)2, etc. The alkali metal hydroxides will be more preferred, with sodium hydroxide being the most preferred of the bases. In general, the pH will be adjusted into a range above 7, more preferably from about 7.5 to about 15, and most preferably from about 12 to about 15.

Reaction Media: Water or mixtures of Water and an alcohol, ketone, ester, amide, sulfoxide, sulfone, etc. will be employed.

Temperature: While not narrowly critical, temperatures in the range from 0 to about 65 C., are preferred, with 10 to 50 C. being more preferred, and 15-40 C. being most preferred. The lower limit is generally the freezing point of the solution and the upper limit is generally the thermal instability point of the gel at the reaction pressure.

Pressure: While not narrowly critical, the reaction can be carried out at pressures of from 0.5 to 100, with 0.6 to 50 being more preferred, and 0.7 to 10 atmospheres being most preferred.

Time: The reaction time, of course, is dependent on the initial concentration of the starting materials and the temperature. The preferred time is from 0.01 to 4500 hours, more preferred 0.05 to 350 hours, and most preferred from 0.06 to 200 hours.

EXAMPLE I Examples Preparation of Polyisocyanurate Salt To a stirred slurry of 82.4 g. KOCN (1.02 mole) in 2000 m1. of dimethylformamide (DMF) at C., 161

g. of tolylene diisocyanate (0.93 mole) is added at a rate of 0.42 mL/mn. by means of a syringe pump.

'Ihe entire operation is carried out in a nitrogen atmosphere. Following the addition, the reaction mixture is stirred an additional 5 minutes, dry methanol added (large excess) and allowed to react for an additional hour to insure complete quenching. The major product is insoluble in DMF and thus readily separated by a single filtration. A trace DMF soluble product is obtained after solvent stripping the filtrate. After vacuum drying at 80 C. to remove residual DMF and methanol, the following yield and analytical data are obtained:

Aryl/end Average Percent group ratio 2 mp1. wt. Product yleldl (ZM-I-N-l-l/M-l-) (minimum) DMF insoluble 3 93. 3 17. 0 8, 000 DMF soluble 6. 3 1. 9 950 1 Corrected for residual DMF. l Measured by nuclear magnetioresonance spectroscopy. l Contains 12.1% DMF of solvatlon.

EXAMPLES II-XI Viscosity of Weight percent 4% by wt. PVA soln., Example PI NaOH PVA cps. Remarks II. 4 2 28-32 White. opaque. III- 4 2 4 55-65 -Do. IV 4 4 4 55-65 White, opaque, 6%

supernatant `qui 4 4 28-32 Blue haze, transparent. 4 4 55-65 Do. 2 5 28-32 White, opaque. 2 5 55-65 Do. 4 5 4-6 D0. 4 5 28-32 Do. 4 5 55-65 DO.

EXAMPLE XII`Corrosiveness To determine whether the gels of the invention were themselves corrosive, a gel prepared according to Example X was measured on a standard instrument called a Corrosometer manufactured by Magna Corporation, Santa Fe Springs, Calif. This instrument uses a wire probe connected to two electrodes. The probe is placed into the material to be studied and the extent of corrosion is measured as a function of time. Corrosion can be measured by virtue of the fact that the formation of oxide coatings on the probe changes the resistance of the probe. This change in resistance is detected by the instrument.

A probe composed of 1018 steel is inserted into a gelled composition prepared according to Example X, above. The resistance of this probe is measured at intervals over a two week period. The results of these measurements indicate that the resistance had not significantly increased over the two week period suggesting that no detectable corrosion has occurred. Visual examination of the probe revealed it to be very clean and uncorroded conrming the non-corrosive nature of the gels.

EXAMPLES XIII-XVII--Corrosiveness of gels on metal coupons A 60-day and a separate 1Z0-day test, otherwise identical are used to determine the longer-term corrosive nature of the gels of the present invention.

Metal coupons of 1018 steel are cleaned by very light Sandblasting, followed by chemical cleaning in a solution of 0.5% SnCl2 and 0.7% SnCla in concentrated hydrochloric acid. Each coupon is allowed to remain in the cleaning solution for 200 seconds with gentle agitation. The coupons are then dried and their initial weights recorded.

The coupons are then divided into iive groups for each of the \60day and 1Z0-day tests. Gel is applied to the coupons of each group in the manners described in Table I. Following application of the gel, each coupon is buried in a separate container of soil taken from Arapahoe County, Colo. Coupons for Examples XIV and XV are placed in a small test tube which is then -illed with sand and the sand subsequently saturated with gelling iiuid at a temperature of about 72 F. After gelation occurs, coupons from the first of these two groups are buried directly. For Example XV, the gel is allowed to dry prior to burying the coupon. Coupons for Examples XVI and XVII are placed in the test tubes and the test tubes filled only with gelling fluid. Example XVI is buried after gelation has occurred. However, for Example XVII, the gel is allowed to d'ry prior to the burial of the coupon.

Once all the coupons are buried in their separate containers, the soil is kept moist for the duration of the test. After the elapse of 60 and 120 days, respectively, the coupons are cleaned by manually removing the soil and chemically cleaning for 400 seconds in a solution identical to that used at the start of the test. (Using fresh coupons, it is established that the weight loss during the cleaning process is 0.02% and this is used to correct the cleaned weights of the test coupons.) The corrected weight loss of he test coupons is shown in Table 1 as percent weight oss.

The gel used was in all cases produced according to Example X, above. Example XIII is the uncoated control.

The gel discussed above provides an elastic coating of substantial thickness which protects the covered areas of the metal coupons from corrosion. 'Ihe coating technique used in these examples is not the most advantageous way of achieving holiday-free coatings. In all cases, holidays were seen to form on the edge of the coupons, because of deciencies in the coating technique. While multiple coating techniques may be known to those skilled in the art which could provide holiday-free coatings which would assure complete corrosion protection, we are teaching here the non-corrosive nature of the gels discussed in Examples II-XI, specifically, Example X. Visual examination of the coupons used in Examples XIV-XVII revealed that in those areas of the coupon surface, where intimate contact had been achieved with the gel composition; protection from corrosion was fairly complete. Corrosion occurs only on the edges of the coupons or where Vholidays have otherwise Ibeen induced.n For example, in Examples XIV and XV it was general rule that the sand grains provided holiday points that are uniformly distributed over the metal coupons, and in all instances the coupon surfaces were seen to be rather uniformly pitted and mild corrosion had occurred. The singular exception to this was in the 1Z0-day test of Example XV where poor contact had been obtained between the sand and the corrodable metal surface. In this case, it appeared that the gel did provide some corrosion protection even in the presence of sand so that a more ethcient coating had apparently been achieved in this particular example. However, from Examples XVI and XVII, visual examination of the coupons revealed that the major part of the surface area was protected from corrosion, and that corrosion did occur only in the vicinity of the coupon edges where, due to the coating process used, it was impossible to achieve a coating of suicient thickness to prevent holidays from developing. These examples demonstrate that, where holiday-free coatings can be achieved, one can achieve complete corrosion protection by the use of the gels produced according to Example X above.

TABLE 1.-CORROSION TEST R is a monovalent hydrocarbon radical or substituted hydrocarbon radical containing from 1 to about 40 carbon atoms, wherein M is the average number of trisubstituted isocyanurate rings per molecule and is a positive number from zero to about 400,

N is the average num-ber of isocyanurate acid and/or is isocyanurate salt groups and is a positive number from above 1 to about 10,000, wherein 2M-}-N-{1=the average number of divalent R groups and is a positive integer from 2 to about 11,0000, and wherein M-l-2 is the average number of A groups and is a positive integer from 2 to about 2,000, and wherein there are Percentiweight loss Weight loss-normal- Severe pitting caused diiculties in cleantng coupons. Consequently this number represents a minimum estimate for corrossoin loss.

Modifications of the Invention It should be understood that the invention is capable of a variety of modifications and variations which will be made apparent to those skilled in the art by a reading of the specification and which are to be included within the spirit of the claims appended hereto.

What is claimed is:

1. A process for protecting metallic objects from corrosion comprising introducing between the surface of said metallic objects and the source of said corrosion, a gel composition substantially insoluble in water prepared by contacting, at a pH 7, a gel formed by reacting about 1.0 to about by weight of polyvinyl alcohol or a precursor thereof at a pH above 7 with from about 0.5 to about 50% by weight of a salt of a polymeric isocyanuric acid, wherein said salt of a polymeric isocyanuric acid has the chemical structure:

R=divalent hydrocarbon or substituted hydrocarbon radical, containing 2 to about 40 carbon atoms,

X is selected from the group consisting of Group I metals, Group II metals, hydrogen, and quaternary ammonium radicals,

A is a monovalent organic radical selected from the no N-to-N bonds and no A-to-N bonds, and no A-to-A bonds and no R-to-R bonds. y2. A process according to Claim 1 wherein R is selected from the group consisting of l @I l @I A@ O COzCH; S-CzHs 0 CH3 0---CH;

03H7 CHg-cH-CHg-CHs (where Hl=F, Cl, Br or I),

0 0 N CH: omocm n-N--cm soicm oe--cm, @j e e @e su@ @N N N CB'a II @Tim-@Cf @@w 5 T CH s' M. NM) 2G C Aralkyl: CH3 g@-m@. NN @CHT., mgm

CH: CH!

Arylaralkyl: @e0-@eene i t 45 @-CIIr-I -C'Hz .0112-, @-(Cli-v ein com.

CH2- H1. 55 H L (Where n may be from 1 to 50) @senese N N @i @n @Q@ N' N COICHI 3. A process according to Claim 1 wherein M is a posi- 70 tive integer from 0 to about 200, wherein N is a positive m v Q integer from 3 to about lO, and wherein 2M+N|1 is a positive integer from 4 to about 140, and wherein M-i-Z is a positive integer from about 2 to about 200. cmg, 4. A process according to Claim 1 wherein R is se- 75 lected from the group consisting of COzOHI elw- 3133 (S: Saturated) C333@ J3 N \N N Alkyl:

1k I: Ara y om `.CMz`@CHz-m -CHl-@KCHa- Arylaralkyl:

N0: @0113-, om C112-, @www Alkene:

1 3- Polymeric:

f CH2- H L n (Where n may be from 1 to 50) Bicyclic:

and the substitute derivatives thereof which are substituted with radicals selected from the group consisting of -NO, Cl, F, Br, I, CN, -CO2R", -CO-R", -O- -SR, -NR"2, -CONR2, SO3R", -SO2R", --SOR", phenyl, naphthyl, alkyl having 1-40 carbon atoms, POaR", cyclohexyl, cyclopropyl, -OCOR,

H -llroon'q where R may be hydrogen or lower alkyl.

5. A process according to Claim 1 wherein R' contains from 1 to l() carbon atoms and is selected from the group consisting of -CHB' -C2H5' C3H7, inc:i HT,

6. A process according to Claim 1 wherein X is selected from the group consisting of: Li, Na, K, hydrogen and quaternary ammonium radicals.

7. An article of manufacture comprising a corrodible metal object, a corrosive moiety, and, sandwiched between said object and said corrosive moiety, a gel formed by reacting about 1.0 to about 10% by weight of polyvinyl alcohol or a precursor thereof at a pH above 7 with from about 0.5 to about 50% by weight of a salt of a polymerized isocyanuric acid having the structure of Claim 1.

8. An article of manufacture comprising a corrodible metal element, corrosive earth, and, sandwiched between said corrodible metal element and said earth, a coating comprising polyvinyl alcohol-polymerized isocyanuric acid said gel prepared from an isocyanurate salt having the structure of Claim 1.

References Cited UNITED STATES PATENTS 7/ 1969 Argabright et al. 260-77.5 NC 3/1971 Arga'bright et al. 252-182 LORENZO B. HAYES, Primary Examiner UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent NO- C 3,843,374 Dated October 22, 1974 Inventor(s) S. Kurtis, et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Figure 2, Line 1, #5: should appear Col. 2, Line 48: "orbanic" should read --organic Col. 3, Line 30: SO3R" should read -SO3R -SO R" should read -SO2- SOR" should read -SO- Col. 3, Line 61: "bottob" should read --bottom Col. 8, Line 13: "11,0000" should read -11,000

Col. 13, Line 24: R should read R" Signed and ealed this [SEAL] tenth Day 0f February 1976 Attest.'

RUTH c. MASON l Atlesling Officer C. MARSHALL DANN Commissioner nfPafenls and Trademark.\`

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,843,374 Dated October 22, 1974 Invent0r(s) S. Kurtis, et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Figure 2, Line l, #5: should appear Col. 2, Line 48: "orbanic" should read organic Col. 3, Line 6l: "bottob" should read bottom Col. 8, Line 13: "11,0000" should read -ll,000

Col'. 13, Line 24: R should read R" ,Signed and Scaled this [SEAL] tenth .Day 0f February 1976 Arrest:

RUTH C. MASON Attesting Officer C. MARSHALL DANN Commissioner of Patents and Trademarks 

1. A PROESSS FOR PROTECTING METALLIC OBJECTS FROM CORROSION COMPRISING INTRODUCING BETWEEN THE SURFACE OF SAID METALLIC OBJECTS AND THE SOURCE OF SAID CORROSION, A GEL COMPOSITION SUBSTANTIALLY INSOLUBLE IN WATER PREPARED BY CONTACTING, AT A PH 7, A GEL FORMED BY REACTING ABOUT 1.0 TO ABTO ABOUT 10% BY WEIGHT OF POLYVINYL ALCOHOL OR A PRECURSOR THEREOF AT A PH ABOVE 7 WITH FORM ABOUT 0.5 TO ABOUT 50% BY WEIGHT OF A SALT OF A POLYMERIC ISOCYANURIC ACID,WHEREIN SAID SALT OF A POLYMERIC ISOCYANURIC ACID HAS THE CHEMICAL STRUCTURE: 